This invention concerns improvements in or relating to infra-red lenses and relates more particularly to an infra-red zoom lens.
There is a requirement for infra-red zoom lenses providing variable magnification for example up to .times.20 or more. Such a lens can be used, in particular, as an objective lens in combination with an "eye-piece" lens to provide an afocal zoom telescope. To date, however, there have been limitations on the use of continuous zoom lenses in some infra-red applications because of the excessive length of the lens.